This invention relates to the Fabry-Perot interference spectrometer. The Fabry-Perot interference spectrometer is characterized especially by high resolving power and brightness and is used particularly for spectral observation necessitating high resolution or involving extremely weak light. Since it generally has a narrow free spectral range (the range in which a spectrum can be observed without overlapping), this interference spectrometer must, however, be used in combination with a pre-dispersing element such as, for example, a diffraction grating, a prism, an interference filter or one or two additional Fabry-Perot interferometers unless it is operated with an intense monochromatic light source. When a diffraction grating or prism is used as the pre-dispersing element, the interference spectrometer provides a darkened spectrum. Incorporation of an interference filter or additional Fabry-Perot interferometer renders the manufacture of the interference spectrometer difficult and necessitates rigid control of the mirror gap during the operation.
An object of the present invention is to provide a Fabry-Perot interference spectrometer which enjoys a notably wide free spectral range without use of a pre-dispersing element.